A method and apparatus for controlling the operation of a microwave oven, including a magnetron generating microwaves and a sensor sensing the state of air in the cooking cavity of the oven. The cooking period is determined by searching one of two data tables in accordance with a determination result after determining whether food to be cooked is included in ascending slope-type foods or descending slope-type foods. The control method and apparatus remarkably reduces a deviation in the cooking periods by distinguishing the ascending slope-type foods from the descending slope-type foods. The control method and apparatus allows the microwave oven to appropriately cook food for a period of time which substantially matches a practically required cooking period, thus providing a good cooking result.